provide way to override east-asian rune width calc (addr. #220) (#223)

Author: jedib0t

text/string.go

@@ -16,6 +16,11 @@ const (
 	EscapeStopRune  = 'm'
 )
 
+// RuneWidth stuff
+var (
+	rwCondition = runewidth.NewCondition()
+)
+
 // InsertEveryN inserts the rune every N characters in the string. For ex.:
 //  InsertEveryN("Ghost", '-', 1) == "G-h-o-s-t"
 //  InsertEveryN("Ghost", '-', 2) == "Gh-os-t"
@@ -79,6 +84,23 @@ func LongestLineLen(str string) int {
 	return maxLength
 }
 
+// OverrideRuneWidthEastAsianWidth can *probably* help with alignment, and
+// length calculation issues when dealing with Unicode character-set and a
+// non-English language set in the LANG variable.
+//
+// Set this to 'false' to force the "runewidth" library to pretend to deal with
+// English character-set. Be warned that if the text/content you are dealing
+// with contains East Asian character-set, this may result in unexpected
+// behavior.
+//
+// References:
+// * https://github.com/mattn/go-runewidth/issues/64#issuecomment-1221642154
+// * https://github.com/jedib0t/go-pretty/issues/220
+// * https://github.com/jedib0t/go-pretty/issues/204
+func OverrideRuneWidthEastAsianWidth(val bool) {
+	rwCondition.EastAsianWidth = val
+}
+
 // Pad pads the given string with as many characters as needed to make it as
 // long as specified (maxLen). This function does not count escape sequences
 // while calculating length of the string. Ex.:
@@ -132,7 +154,7 @@ func RuneCount(str string) int {
 //  RuneWidth('︿') == 2
 //  RuneWidth(0x27) == 0
 func RuneWidth(r rune) int {
-	return runewidth.RuneWidth(r)
+	return rwCondition.RuneWidth(r)
 }
 
 // RuneWidthWithoutEscSequences is similar to RuneWidth, except for the fact

text/string_test.go

@@ -80,6 +80,27 @@ func TestLongestLineLen(t *testing.T) {
 	assert.Equal(t, 7, LongestLineLen("\x1b[33mMother\x1b[0m\nOf\nDragons"))
 }
 
+func TestOverrideRuneWidthEastAsianWidth(t *testing.T) {
+	originalValue := rwCondition.EastAsianWidth
+	defer func() {
+		rwCondition.EastAsianWidth = originalValue
+	}()
+
+	OverrideRuneWidthEastAsianWidth(true)
+	assert.Equal(t, 2, RuneWidthWithoutEscSequences("╋"))
+	OverrideRuneWidthEastAsianWidth(false)
+	assert.Equal(t, 1, RuneWidthWithoutEscSequences("╋"))
+
+	// Note for posterity. We want the length of the box drawing character to
+	// be reported as 1. However, with an environment where LANG is set to
+	// something like 'zh_CN.UTF-8', the value being returned is 2, which breaks
+	// text alignment/padding logic in this library.
+	//
+	// If a future version of runewidth is able to address this internally and
+	// return 1 for the above, the function being tested can be marked for
+	// deprecation.
+}
+
 func ExamplePad() {
 	fmt.Printf("%#v\n", Pad("Ghost", 0, ' '))
 	fmt.Printf("%#v\n", Pad("Ghost", 3, ' '))